1. Technical Field of the Invention
The present invention relates to novel cosmetic and/or dermatological compositions comprising at least one iron oxide nanopigment, well suited for artificially tanning and/or darkening human skin to such extent as to resemble a natural tan.
2. Description of the Prior Art
Today, many consumers seek to retain a healthy appearance and desire a tanned skin. However, natural tanning is not always desirable insofar as it requires prolonged exposure to UV radiation, in particular to UV-A radiation, which promotes browning of the skin but, on the other hand, can induce a detrimental change in the latter, in particular in the case of sensitive skin or of skin continually exposed to solar radiation. It is therefore desirable to provide an alternative to natural tanning which is compatible with the requirements of such skin.
The majority of cosmetic products suited for the artificial tanning of the skin are based on carbonyl compounds which enable the formation of colored species by interaction with the amino acids of the skin.
To this end, it is known to this art that dihydroxyacetone, or DHA, is a particularly advantageous active species which is commonly used in cosmetics as an agent for the artificial tanning of the skin; applied to the skin, in particular to the face, it makes it possible to obtain a tanning or browning effect with an appearance similar to that which can result from prolonged exposure to the sun (natural tanning) or under a UV lamp.
However, the use of DHA can present certain disadvantages. Thus, DHA has an unfortunate tendency, more or less pronounced depending on the nature of the medium in which it is formulated, to decompose over time, this decomposition generally being reflected in the long run by an undesirable yellowing of the compositions in which it is present. Such a phenomenon indicates that the activity of the DHA, in particular its ability to color the skin, may be decreased at the time of the application of these compositions onto the skin. Thus, the intensity of the coloration imparted to the skin may appear to remain insufficient.
Another disadvantage of DHA is the slowness with which the coloration develops: this is because several hours (3 to 5 hours in general) are required for the coloring to develop. Furthermore, the coloring produced on the skin with DHA is often regarded as too yellow by users.
Responding to this need, it has been suggested to combine DHA with various compounds: thus, WO-95/15742 describes the combination of DHA with amino acids. However, such combinations are very little used in practice insofar as such use requires either a two-step application or complex separate packagings. FR-2,726,761 describes, for its part, the combination of DHA with lawsone and/or juglone; here again, this combination is not very satisfactory, due this time to the risks of sensitization which it exhibits.
Thus, serious need continues to exist for novel compounds and novel compositions which make it possible to artificially confer on the skin a coloration similar to natural tanning in a simple, efficient, rapid and risk-free manner.
Iron oxide pigments have long been known for their superficial and short-lived covering and coloring properties on human skin. They are generally formulated into makeup products, such as foundations, mascaras, eyeliners and lipsticks. Their mean size generally ranges from 0.2 to 50 .mu.m depending on the desired coloring effects and the application envisaged. Exemplary of the makeup compositions comprising same are described in WO-94/15580, WO-96/36309, WO-96/33690, WO-96/36323 and FR-A-2,754,708.
Iron oxide nanoparticles (hereinafter referred to as iron oxide nanopigments) having a mean size of less than 200 nm are generally used for their good properties of screening UV radiation over a large spectrum in the formulation of cosmetic compositions, such as those described in FR-A-2,746,301 and FR-A-2,746,301. They are also present in sun protection products based on titanium or zinc oxide nanopigments, in order to lighten or mask the blue color resulting from photobluing under the influence of UV radiation, as described in WO-93/11742.